Method of operating semiconductor apparatus and semiconductor apparatus

ABSTRACT

A method of operating a semiconductor apparatus includes generating a target material droplet; exciting the target material droplet to generate radiation for exposing a wafer; receiving, by a catcher, the target material droplet after exciting the target material droplet, in which the catcher has a front section, a rear section, and a drain port at the rear section; heating the rear section of the catcher such that the target material droplet in the rear section is in a liquid phase; and maintaining a temperature of the front section of the catcher lower than a temperature of the rear section of the catcher.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Application Ser.No. 62/690,081, filed on Jun. 26, 2018, which is herein incorporated byreference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofIC processing and manufacturing. For example, higher resolutionlithography processes have been developed. One lithography technique isextreme ultraviolet lithography (EUVL).

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic view of an extreme ultraviolet (EUV) lithographysystem in accordance with some embodiments of the present disclosure;

FIG. 2 is a side view of a semiconductor apparatus of FIG. 1;

FIG. 3 is a flow chart of a method of operating a semiconductorapparatus in accordance with some embodiments of the present disclosure;

FIG. 4 is a top view of a droplet catcher and a heater of FIG. 2;

FIG. 5 is a cross-sectional view of the droplet catcher and the heatertaken along line 5-5 of FIG. 4 when receiving target material droplets;

FIG. 6 is a cross-sectional view of a droplet catcher and two heaters inaccordance with some embodiments of the present disclosure whenreceiving target material droplets;

FIG. 7 is a flow chart of a method of operating a semiconductorapparatus in accordance with some embodiments of the present disclosure;and

FIG. 8 is a cross-sectional view of a droplet catcher, a heater, and acooling system in accordance with some embodiments of the presentdisclosure when receiving target material droplets.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

FIG. 1 is a schematic view of an extreme ultraviolet (EUV) lithographysystem 10 in accordance with some embodiments of the present disclosure.The lithography system 10 may also be generically referred to as ascanner that is operable to perform lithography exposing processes withrespective radiation source and exposure mode. In some embodiments, thelithography system 10 is an extreme ultraviolet (EUV) lithography systemdesigned to expose a resist layer by EUV light. The resist layer is amaterial sensitive to the EUV light. The EUV lithography system 10employs a semiconductor apparatus 100 to generate EUV light, such as EUVlight having a wavelength ranging between about 1 nm and about 100 nm.In some embodiments, the semiconductor apparatus 100 generates EUV lightwith a wavelength centered at about 13.5 nm. Accordingly, thesemiconductor apparatus 100 is referred to as an EUV radiation source.In some embodiments, the semiconductor apparatus 100 utilizes amechanism of laser-produced plasma (LPP) to generate the EUV radiation,which will be further described later.

The lithography system 10 also employs an illuminator 14. In variousembodiments, the illuminator 14 includes various refractive opticcomponents, such as a single lens or a lens system having multiplelenses (zone plates) or alternatively reflective optics (for EUVlithography system), such as a single mirror or a mirror system havingmultiple mirrors in order to direct light from the semiconductorapparatus 100 onto a mask stage 16, or onto a mask 18 secured on themask stage 16. In some embodiments where the semiconductor apparatus 100generates light in the EUV wavelength range, reflective optics isemployed.

The lithography system 10 also includes the mask stage 16 configured tosecure a mask 18. In some embodiments, the mask stage 16 includes anelectrostatic chuck (e-chuck) to secure the mask 18. This is becausethat gas molecules absorb EUV light and the lithography system for theEUV lithography patterning is maintained in a vacuum environment toavoid the EUV intensity loss. In the present disclosure, the terms ofmask, photomask, and reticle are used to refer to the same item. In someembodiments, the lithography system 10 is an EUV lithography system, andthe mask 18 is a reflective mask. The mask 18 is provided forillustration. The mask 18 includes a substrate with a suitable material,such as a low thermal expansion material (LTEM) or fused quartz. Invarious examples, the LTEM includes TiO₂ doped SiO₂, or other suitablematerials with low thermal expansion. The mask 18 includes a multiplereflective multiple layers (ML) deposited on the substrate. The MLincludes a plurality of film pairs, such as molybdenum-silicon (Mo/Si)film pairs (e.g., a layer of molybdenum above or below a layer ofsilicon in each film pair). Alternatively, the ML may includemolybdenum-beryllium (Mo/Be) film pairs, or other suitable materialsthat are configurable to highly reflect the EUV light. The mask 18 mayfurther include a capping layer, such as ruthenium (Ru), disposed on theML for protection. The mask 18 further includes an absorption layer,such as a tantalum boron nitride (TaBN) layer, deposited over the ML.The absorption layer is patterned to define a layer of an integratedcircuit (IC). Alternatively, another reflective layer may be depositedover the ML and is patterned to define a layer of an integrated circuit,thereby forming an EUV phase shift mask.

The lithography system 10 also includes a projection optics module (orprojection optics box (POB) 20 for imaging the pattern of the mask 18 onto a semiconductor wafer 22 secured on a substrate stage 24 of thelithography system 10. The POB 20 has refractive optics (such as for UVlithography system) or alternatively reflective optics (such as for EUVlithography system) in various embodiments. The light directed from themask 18, carrying the image of the pattern defined on the mask, iscollected by the POB 20. The illuminator 14 and the POB 20 arecollectively referred to an optical module of the lithography system 10.

The lithography system 10 also includes the substrate stage 24 to securethe semiconductor wafer 22. In some embodiments, the semiconductor wafer22 may be a silicon wafer or other type of wafer to be patterned. Thesemiconductor wafer 22 is coated with the resist layer sensitive to theradiation beam, such as EUV light in some embodiments. Variouscomponents including those described above are integrated together andare operable to perform lithography exposing processes. The lithographysystem 10 may further include other modules or be integrated with (or becoupled with) other modules. In some embodiments, the lithography system10 includes a gas supply module to provide hydrogen gas to thesemiconductor apparatus 100.

FIG. 2 is a side view of the semiconductor apparatus 100 of FIG. 1. Thesemiconductor apparatus 100 includes a laser 30, a collector 36, adroplet generator 110, and a droplet catcher 120. The collector 36 isabove the laser 30, and the droplet generator 110 and the dropletcatcher 120 are above the collector 36. The droplet catcher 120 facesthe droplet generator 110. The semiconductor apparatus 100 employs alaser produced plasma (LPP) mechanism to generate plasma and furthergenerate EUV light from the plasma. The laser 30, such as pulse carbondioxide (CO2) laser, is configured to generate a laser beam 32. Thelaser beam 32 is directed through an output window 34 integrated withthe collector 36 (also referred to as LPP collector or EUV collector).The output window 34 adopts a suitable material substantiallytransparent to the laser beam. The collector 36 is designed with propercoating material and shape, functioning as a mirror for EUV collection,reflection and focus. In some embodiments, the collector 36 is designedto have an ellipsoidal geometry. In some embodiments, the coatingmaterial of the collector 36 is similar to the reflective multilayer ofthe EUV mask 18 (see FIG. 1). In some examples, the coating material ofthe collector 36 includes a ML (such as a plurality of Mo/Si film pairs)and may further include a capping layer (such as Ru) coated on the ML tosubstantially reflect the EUV light. In some embodiments, the collector36 may further include a grating structure designed to effectivelyscatter the laser beam directed onto the collector 36. For example, asilicon nitride layer is coated on the collector 36 and is patterned tohave a grating pattern.

The laser beam 32 is directed to heat target material droplets 38, suchas tin droplets, thereby generating high-temperature plasma, whichfurther produces EUV radiation 40 (or EUV light). The EUV radiation 40is collected by the collector 36. The collector 36 further reflects andfocuses the EUV radiation 40 for the lithography exposing processes. Thelaser beam 32 is focused to the target material droplets 38, such as tindroplets, thereby generating high-temperature plasma. The targetmaterial droplets 38 are generated by the droplet generator 110. Thedroplet catcher 120 is further configured to catch the target materialdroplets 38. Thus generated high-temperature plasma further produces EUVradiation 40, which is collected by the collector 36. The collector 36further reflects and focuses the EUV radiation 40 for the lithographyexposing processes. The pulses of the laser 30 and the dropletgenerating rate of the droplet generator 110 are controlled to besynchronized such that the target material droplets 38 receive peakpowers consistently from the laser pulses of the laser 30. The laser 30and the droplet generator 110 are turned on in a synchronized mode (thelaser pulse and the tin generation rate are synchronized) through asuitable mechanism, such as a control circuit with timer to control andsynchronize the both. In some embodiments, the EUV radiation 40generated by the semiconductor apparatus 100 is illuminated on the mask18 (by the illuminator 14), and is further projected on the resist layercoated on the wafer 22 (by the POB 20), thereby forming a latent imageon the resist layer.

In addition, the semiconductor apparatus 100 is configured in anenclosed space (referred to as a source vessel). The source vessel ismaintained in a vacuum environment since the air absorbs the EUVradiation 40. The semiconductor apparatus 100 may further be integratedwith or coupled with other units/modules. For example, a gas supplymodule may be coupled with the semiconductor apparatus 100, therebyproviding hydrogen gas to prevent the collector 36 from thecontaminations of the target material droplets 38 (e.g., tin particlesor tin debris).

FIG. 3 is a flow chart of a method of operating a semiconductorapparatus in accordance with some embodiments of the present disclosure.The method begins with block 210 in which a target material droplet isgenerated. The method continues with block 220 in which the targetmaterial droplet is excited to generate radiation for exposing a wafer.The method continues with block 230 in which the target material dropletis received by a catcher after exciting the target material droplet, andthe catcher has a front section, a rear section, and a drain port at therear section. The method continues with block 240 in which the rearsection of the catcher is heated such that the target material dropletin the rear section is in a liquid phase. The method continues withblock 250 in which a temperature of the front section of the catcher ismaintained to be lower than a temperature of the rear section of thecatcher. While the method is illustrated and described below as a seriesof acts or events, it will be appreciated that the illustrated orderingof such acts or events are not to be interpreted in a limiting sense.For example, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the description herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

Reference is made to FIG. 2, the target material droplets 38 aregenerated by the droplet generator 110, and then the target materialdroplets 38 are excited to generate the radiation 40 for exposing thewafer 22 (see FIG. 1). After the target material droplets 38 areexcited, the droplet catcher 120 receives the target material droplets38. In the following description, structures of the droplet catcher 120and a heater 130 of the semiconductor apparatus 100 and method ofcatching the target material droplets 38 will be described.

FIG. 4 is a top view of the droplet catcher 120 and the heater 130 ofFIG. 2. The droplet catcher 120 includes a front section 122 and a rearsection 124 that adjoins the front section 122. An end of the frontsection 122 distal to the rear section 124 has an opening O to receivethe target material droplets 38 (see FIG. 2). The heater 130 isconfigured to heat the rear section 124 of the droplet catcher 120, suchthat the front section 122 of the droplet catcher 120 has a temperaturelower than a temperature of the rear section 124 of the droplet catcher120. In some embodiments, the heater 130 includes a heating coil 132around an outer surface 121 of the rear section 124 of the dropletcatcher 120, but the present disclosure is not limited in this regard.Moreover, in some embodiments, the front section 122 of the dropletcatcher 120 has no heater thereon, and the front section 122 receivesheat from the rear section 124 through heat conduction and heatradiation, which results in heat dissipation. Therefore, the temperatureof the front section 122 of the droplet catcher 120 is lower than thetemperature of the rear section 124 of the droplet catcher 120. In someembodiments, the temperatures of the front section 122 and the rearsection 124 of the droplet catcher 120 are maintained by the heater 130.

FIG. 5 is a cross-sectional view of the droplet catcher 120 and theheater 130 taken along line 5-5 of FIG. 4 when receiving the targetmaterial droplets 38. The rear section 124 of the droplet catcher 120 isheated by the heater 130 such that the target material droplets 38 inthe rear section 124 are in a liquid phase. Further, the temperature ofthe front section 122 of the droplet catcher 120 is maintained to belower than the temperature of the rear section 124 of the dropletcatcher 120. In some embodiments, the temperature of the front section122 of the droplet catcher 120 is higher than a melting point of thetarget material droplets 38. For example, the target material droplets38 are tin droplets, and the melting point of the target materialdroplets 38 is in a range about 231° C. to about 232° C.

After the target material droplets 38 enter the droplet catcher 120through the opening O, the target material droplets 38 may hit an innersurface 123 of the front section 122 of the droplet catcher 120.According to the physical property of tin, if the target materialdroplets 38 are tin droplets and have a temperature higher than themelting point of tin but lower than the boiling point of tin, theviscosity of the tin droplets 38 increases as the temperature of the tindroplets 38 decreases. In some embodiments, the temperature of the frontsection 122 of the droplet catcher 120 is lower than about 233° C. Insome embodiments, the inner surface 123 of the front section 122 of thedroplet catcher 120 is maintained in a temperature range from about231.9° C. to about 233° C. Because the inner surface 123 of the frontsection 122 of the droplet catcher 120 is maintained in the temperaturerange, the target material droplets 38 can be cooled down to increasethe viscosity thereof and in a liquid phase. In some embodiments, thetarget material droplets 38 in the front section 122 of the dropletcatcher 120 have the viscosity in a range from about 1.5 mPa·s to about2.0 mPa·s. As a result, the cooled target material droplets 38 in thefront section 122 of the droplet catcher 120 have the increasedviscosity, and thus the cooled target material droplets 38 can flow intothe rear section 124 of the droplet catcher 120 along the inner surface123 of the front section 122 without reversely splashing.

Moreover, the temperature of the rear section 124 of the droplet catcher120 is lower than a boiling point of the target material droplets 38.For example, the target material droplets 38 are tin droplets, and theboiling point of the target material droplets 38 is in a range about2602° C. to about 2603° C. After the target material droplets 38 flowinto the rear section 124 of the droplet catcher 120, the targetmaterial droplets 38 attached to the inner surface 123 are near theheater 130. In some embodiments, the temperature of the rear section 124of the droplet catcher 120 is higher than about 2600.9° C. In someembodiments, the inner surface 123 of the rear section 124 of thedroplet catcher 120 is maintained in a temperature range from about2600.9° C. to about 2601.9° C. Because the inner surface 123 of the rearsection 124 of the droplet catcher 120 is maintained in the temperaturerange, the target material droplets 38 can be heated up to decrease theviscosity thereof and in a liquid phase. In some embodiments, the targetmaterial droplets 38 in the rear section 124 of the droplet catcher 120have the viscosity in a range from about 0.5 mPa·s to about 1.0 mPa·s.The target material droplets 38 in the rear section 124 of the dropletcatcher 120 have a lower viscosity than the target material droplets 38in the front section 122 of the droplet catcher 120. As a result, theheated target material droplets 38 in the rear section 124 of thedroplet catcher 120 have the decreased viscosity, and thus the heatedtarget material droplets 38 can be easily collected by rear section 124of the droplet catcher 120 due to good fluidity, thereby preventingreversely splashing.

In some embodiments, the droplet catcher 120 has a drain port 125 at therear section 124 of the droplet catcher 120. The target materialdroplets 38 may be recycled from the rear section 124 of the dropletcatcher 120 to the droplet generator 110 of FIG. 2 through the drainport 125.

Reference is made to FIG. 4, the front section 122 of the dropletcatcher 120 is longer than the rear section 124 of the droplet catcher120. In other words, a length L1 of the front section 122 of the dropletcatcher 120 is greater than a length L2 of the rear section 124 of thedroplet catcher 120. The droplet catcher 120 has a total length L3substantially equal to the sum of the length L1 of the front section 122and the length L2 of the rear section 124. In some embodiments, thelength L1 of the front section 122 of the droplet catcher 120 is in arange from about 80% of the total length L3 to about 85% of the totallength L3. On the other hand, the length L2 of the rear section 124 ofthe droplet catcher 120 is in a range from about 15% of the total lengthL3 to about 20% of the total length L3. As a result of such aconfiguration, the front section 122 of the droplet catcher 120 hasenough distance to cool the target material droplets 38 (see FIG. 5),such that the target material droplets 38 can be prevented fromreversely splashing.

Reference is made to FIG. 5, the semiconductor apparatus 100 (see FIG.2) further includes a sensor 140 a, a sensor 140 b, and a controller C.The controller C is electrically connected to the sensor 140 a, thesensor 140 b, and the heater 130. The sensor 140 a and the sensor 140 bare respectively in the front section 122 and the rear section 124 ofthe droplet catcher 120, and are adjacent to the inner surface 123. Thesensor 140 a is configured to detect the temperature of the innersurface 123 of the front section 122 of the droplet catcher 120, and thesensor 140 b is configured to detect the temperature of the innersurface 123 of the rear section 124 of the droplet catcher 120. Thecontroller C is configured to control the heater 130 according to thedetected temperature of the inner surface 123 of the front section 122and the rear section 124 of the droplet catcher 120. In some embodiment,the controller C can control the heater 130 such that the inner surface123 of the front section 122 of the droplet catcher 120 is in atemperature range from about 231.9° C. to about 233° C., and the innersurface 123 of the rear section 124 of the droplet catcher 120 is in atemperature range from about 2600.9° C. to about 2601.9° C. The numberof coils of the heater 130, the length L1 of the front section 122, andthe length L2 of the rear section 124 (see FIG. 4) may be varied as longas the inner surface 123 of the front section 122 and the inner surface123 of the rear section 124 respectively have the two aforementionedtemperature ranges.

It is to be noted that the connection relationships of the elementsdescribed above will not be repeated in the following description. Inthe following description, other types of droplet catchers will bedescribed.

FIG. 6 is a cross-sectional view of the droplet catcher 120 and twoheaters 130 and 130 a in accordance with some embodiments of the presentdisclosure when receiving the target material droplets 38. Thesemiconductor apparatus 100 (see FIG. 2) further includes the heater 130a, a controller C1, and a controller C2. The heater 130 a is configuredto maintain the temperature of the front section 122 of the dropletcatcher 120 higher than the melting point of the target materialdroplets 38, but lower than the temperature of the rear section 124 ofthe droplet catcher 120. In some embodiments, the heater 130 a includesa heating coil 132 a around the outer surface 121 of the front section122 of the droplet catcher 120. The controller C1 is electricallyconnected to the sensor 140 a and the heater 130 a, and the controllerC2 is electrically connected to the sensor 140 b and the heater 130. Thecontroller C1 is configured to control the heater 130 a according to thedetected temperature of the inner surface 123 of the front section 122of the droplet catcher 120, and the controller C2 is configured tocontrol the heater 130 according to the detected temperature of theinner surface 123 of the rear section 124 of the droplet catcher 120. Insome embodiment, the controller C1 can control the heater 130 a suchthat the inner surface 123 of the front section 122 of the dropletcatcher 120 is in a temperature range from about 231.9° C. to about 233°C., and the controller C2 can control the heater 130 such that the innersurface 123 of the rear section 124 of the droplet catcher 120 is in atemperature range from about 2600.9° C. to about 2601.9° C. As a resultof such a configuration, the target material droplets 38 in the frontsection 122 of the droplet catcher 120 has a higher viscosity than thetarget material droplets 38 in the rear section 124 of the dropletcatcher 120, thereby preventing the target material droplets 38 fromreversely splashing onto the collector 36 (see FIG. 2) outside thedroplet catcher 120 to cause contamination.

FIG. 7 is a flow chart of a method of operating a semiconductorapparatus in accordance with some embodiments of the present disclosure.The method begins with block 310 in which a target material droplet isgenerated. The method continues with block 320 in which the targetmaterial droplet is excited to generate radiation for exposing a wafer.The method continues with block 330 in which the target material dropletis received by a catcher after exciting the target material droplet, andthe target material droplet received by the catcher hits an innersurface of a front section of the catcher and then flows into a rearsection of the catcher. The method continues with block 340 in which theinner surface of the front section of the catcher is maintained in afirst temperature range, such that the target material droplet is cooleddown and in a liquid phase when hitting the inner surface of the frontsection of the catcher. The method continues with block 350 in which therear section of the catcher is maintained in a second temperature range,such that the target material droplet is heated up and in the liquidphase when flowing into the rear section of the catcher. While themethod is illustrated and described below as a series of acts or events,it will be appreciated that the illustrated ordering of such acts orevents are not to be interpreted in a limiting sense. For example, someacts may occur in different orders and/or concurrently with other actsor events apart from those illustrated and/or described herein. Inaddition, not all illustrated acts may be required to implement one ormore aspects or embodiments of the description herein. Further, one ormore of the acts depicted herein may be carried out in one or moreseparate acts and/or phases.

FIG. 8 is a cross-sectional view of the droplet catcher 120, the heater130, and a cooling system 150 in accordance with some embodiments of thepresent disclosure when receiving the target material droplets 38. Thetarget material droplets 38 are generated by the droplet generator 110of FIG. 2, and then the target material droplets 38 are excited togenerate the radiation 40 for exposing the wafer 22 (see FIG. 1). Afterthe target material droplets 38 are excited, the target materialdroplets 38 are received by the droplet catcher 120, and the targetmaterial droplets 38 hit the inner surface 123 of the front section 122of the droplet catcher 120 and then flow into the rear section 124 ofthe droplet catcher 120. In some embodiments, the semiconductorapparatus 100 of FIG. 2 further includes a cooling system 150 configuredto cool the front section 122 of the droplet catcher 120. The coolingsystem 150 may comprise a recirculating cooling liquid system 151. Insome embodiments, the recirculating cooling liquid system 151 includes apump 152, pipes 154, and working fluid F in the pipes 154. The pump 152may be a liquid cooling pump, such as a water cooling pump. The workingfluid F may be water, but the present disclosure is not limited in thisregard. The pipes 154 are connected to the pump 152 and the frontsection 122 of the droplet catcher 120. Portions of the pipes 154 in thefront section 122 of the droplet catcher 120 are disposed along theinner surface 123 of the front section 122, such as substantiallyparallel to the inner surface 123 of the front section 122. Furthermore,the portions of the pipes 154 in the front section 122 are adjacent tothe inner surface 123 of the front section 122 for better heatdissipation rate.

As a result of such a configuration, when the pump 152 is in operation,the working fluid F can flow along the inner surface 123 of the frontsection 122 in a direction D, such that the inner surface 123 of thefront section 122 of the droplet catcher 120 can be maintained in atemperature range, such as in the temperature range from about 231.9° C.to about 233° C. In other words, the temperature of the front section122 of the droplet catcher 120 are maintained using the recirculatingcooling liquid system 151. As a result, the target material droplets 38are cooled down to increase the viscosity thereof and are in a liquidphase when hitting the inner surface 123 of the front section 122 of thedroplet catcher 120. Accordingly, the target material droplets 38 canflow into the rear section 124 of the droplet catcher 120 along theinner surface 123 of the front section 122 due to the increasedviscosity, thereby preventing the target material droplets 38 fromreversely splashing onto the collector 36 (see FIG. 2) outside thedroplet catcher 120 to cause contamination.

In addition, the semiconductor apparatus 100 of FIG. 2 further includesa controller C3. The controller C3 is electrically connected to the pump152 and the sensor 140 a. The sensor 140 a is configured to detect thetemperature of the inner surface 123 of the front section 122 of thedroplet catcher 120, and the controller C3 is configured to control thecooling system 150 (e.g., the pump 152) according to the detectedtemperature of the inner surface 123 of the front section 122 of thedroplet catcher 120. In some embodiments, when the temperature of thefront section 122 of the droplet catcher 120 is higher than about 232.9°C., a cooling liquid flow rate of the recirculating cooling liquidsystem 151 is increased by the pump 152. On the other hand, when thetemperature of the front section 122 of the droplet catcher 120 is lowerthan about 232° C., a cooling liquid flow rate of the recirculatingcooling liquid system 151 is decreased by the pump 152.

Moreover, the rear section 124 of the droplet catcher 120 is maintainedin another temperature range, such that the target material droplets 38are heated up and in the liquid phase when flowing into the rear section124 of the droplet catcher 120. The controller C2 is electricallyconnected to the sensor 140 b and the heater 130, and is configured tocontrol the heater 130 according to the temperature of the inner surface123 of the rear section 124 detected by the sensor 140 b. In someembodiment, the controller C2 can control the heater 130 such that theinner surface 123 of the rear section 124 of the droplet catcher 120 isin a temperature range from about 2600.9° C. to about 2601.9° C. Thetarget material droplets 38 in the rear section 124 of the dropletcatcher 120 have a lower viscosity than the target material droplets 38in the front section 122 of the droplet catcher 120. As a result, theheated target material droplets 38 in the rear section 124 of thedroplet catcher 120 have the decreased viscosity, and thus the heatedtarget material droplets 38 can be easily collected by rear section 124of the droplet catcher 120 due to good fluidity, thereby preventingreversely splashing.

In some embodiments, the droplet catcher has the front section with alow temperature and the rear section with a high temperature, in whichthe low temperature of the front section is higher than the meltingpoint of the target material droplets, and the high temperature of therear section is lower than the boiling point of the droplets. After thedroplet catcher receives the target material droplets, the targetmaterial droplets hit the inner surface of the front section of thedroplet catcher, such that the target material droplets have increasedviscosity in the front section. Thereafter, the target material dropletscan flow into the rear section along the inner surface of the frontsection, and are heated up in the rear section for collection, therebypreventing the target material droplets from reversely splashing.

According to some embodiments, a method of operating a semiconductorapparatus includes generating a target material droplet; exciting thetarget material droplet to generate radiation for exposing a wafer;receiving, by a catcher, the target material droplet after exciting thetarget material droplet, in which the catcher has a front section, arear section, and a drain port at the rear section; heating the rearsection of the catcher such that the target material droplet in the rearsection is in a liquid phase; and maintaining a temperature of the frontsection of the catcher lower than a temperature of the rear section ofthe catcher.

According to some embodiments, a method of operating a semiconductorapparatus includes generating a target material droplet; exciting thetarget material droplet to generate radiation for exposing a wafer;receiving, by a catcher, the target material droplet after exciting thetarget material droplet, wherein the target material droplet received bythe catcher hits an inner surface of a front section of the catcher andthen flows into a rear section of the catcher; maintaining the innersurface of the front section of the catcher in a first temperaturerange, such that the target material droplet is cooled down and in aliquid phase when hitting the inner surface of the front section of thecatcher; and maintaining the rear section of the catcher in a secondtemperature range, such that the target material droplet is heated upand in the liquid phase when flowing into the rear section of thecatcher.

According to some embodiments, a semiconductor apparatus includes adroplet generator, a droplet catcher, a heater, and a cooling system.The droplet catcher faces the droplet generator, and includes a rearsection and a front section between the rear section and the dropletgenerator. The heater is configured to heat the rear section of thedroplet catcher. The cooling system is configured to cool the frontsection of the droplet catcher.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not de depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: generating a targetmaterial droplet; exciting the target material droplet to generateradiation for exposing a wafer; receiving, by a catcher, the targetmaterial droplet after exciting the target material droplet, wherein thecatcher has a front section, a rear section, and a drain port at therear section; heating the rear section of the catcher such that thetarget material droplet in the rear section is in a liquid phase; andmaintaining a temperature of the front section of the catcher lower thana temperature of the rear section of the catcher.
 2. The method of claim1, wherein the temperature of the front section of the catcher is higherthan a melting point of the target material droplet.
 3. The method ofclaim 2, wherein the temperature of the front section of the catcher islower than about 233° C.
 4. The method of claim 1, wherein thetemperature of the rear section of the catcher after heating the rearsection of the catcher is lower than a boiling point of the targetmaterial droplet.
 5. The method of claim 4, wherein the temperature ofthe rear section of the catcher is higher than about 2600.9° C.
 6. Themethod of claim 1, wherein the front section of the catcher is longerthan the rear section of the catcher.
 7. The method of claim 1, whereinmaintaining the temperature of the front section of the catcher isperformed using a recirculating cooling liquid system.
 8. The method ofclaim 7, wherein maintaining the temperature of the front section of thecatcher comprises: increasing a cooling liquid flow rate of therecirculating cooling liquid system when the temperature of the frontsection of the catcher is higher than about 232.9° C.
 9. The method ofclaim 7, wherein maintaining the temperature of the front section of thecatcher comprises: decreasing a cooling liquid flow rate of therecirculating cooling liquid system when the temperature of the frontsection of the catcher is lower than about 232° C.
 10. A method,comprising: generating a target material droplet; exciting the targetmaterial droplet to generate radiation for exposing a wafer; receiving,by a catcher, the target material droplet after exciting the targetmaterial droplet, wherein the target material droplet received by thecatcher hits an inner surface of a front section of the catcher and thenflows into a rear section of the catcher; maintaining the inner surfaceof the front section of the catcher in a first temperature range, suchthat the target material droplet is cooled down and in a liquid phasewhen hitting the inner surface of the front section of the catcher; andmaintaining the rear section of the catcher in a second temperaturerange, such that the target material droplet is heated up and in theliquid phase when flowing into the rear section of the catcher.
 11. Themethod of claim 10, further comprising: recycling the target materialdroplet from the rear section of the catcher to a droplet generator. 12.The method of claim 10, wherein the target material droplet in the frontsection of the catcher has a higher viscosity than the target materialdroplet in the rear section of the catcher.
 13. The method of claim 10,wherein the target material droplet in the front section of the catcherhas a viscosity in a range from about 1.5 mPa·s to about 2.0 mPa·s. 14.The method of claim 10, wherein the target material droplet in the rearsection of the catcher has a viscosity in a range from about 0.5 mPa·sto about 1.0 mPa·s.
 15. An apparatus, comprising: a droplet generator; adroplet catcher facing the droplet generator, the droplet catchercomprising a rear section and a front section between the rear sectionand the droplet generator; a heater configured to heat the rear sectionof the droplet catcher; and a cooling system configured to cool thefront section of the droplet catcher.
 16. The apparatus of claim 15,wherein the front section of the droplet catcher is longer the rearsection of the droplet catcher.
 17. The apparatus of claim 15, whereinthe cooling system comprises a recirculating cooling liquid system. 18.The apparatus of claim 15, further comprising: a sensor configured todetect a temperature of an inner surface of the front section of thedroplet catcher; and a controller configured to control the coolingsystem according to the detected temperature of the inner surface of thefront section of the droplet catcher.
 19. The apparatus of claim 15,further comprising: a sensor configured to detect a temperature of aninner surface of the rear section of the droplet catcher; and acontroller configured to control the heater according to the detectedtemperature of the inner surface of the rear section of the dropletcatcher.
 20. The apparatus of claim 15, wherein the heater comprises aheating coil around an outer surface of the rear section of the dropletcatcher.